Modular low air loss patient support system and methods for automatic patient turning and pressure point relief

ABSTRACT

A low air loss patient support system includes a plurality of identical multi-chambered inflatable sacks. A restrictive flow hole connects two adjacent chambers disposed predominately to one side of the centerline of the sack, and each side is separately pressurizable under the control of a microprocessor and a plurality of pressure control valves with pressure transducers and a plurality of flow diverter valves for switching between different modes of configuring the manner in which the sacks are pressurized. The system includes a modular manifold for mounting the pressure control valves, and a modular support member for mounting the sacks via quick-disconnect couplings and having air flow channels defined therethrough. The support system effects a method of rotating or tilting the patient that depressurizes one side of the sacks while increasing the pressurization of the opposite side of the sacks. The end chamber of the depressurizing side of the sacks remains inflated while the intermediate chamber of the depressurizing side of the sacks becomes progressively deflated during depressurization to permit the end chamber to restrain the patient from sliding off the sacks during tilting. The support system permits practicing the method of relieving pressure points between the patient and the sacks while elevating the head and chest of the patient by reconfiguring the diverter valves to connect alternating sacks at the same pressure and periodically decreasing the pressure in one group of sacks while increasing the pressure in the other group of sacks to alternately relieve the pressure of the weight of the patient between the two different groups of sacks depending upon which group is depressurizing and which group is being increased in pressure.

BACKGROUND OF THE INVENTION

The present invention relates to patient support systems and moreparticularly to a low air loss patient support system. This applicationis a Continuation-In-Part of Application Ser. No. 07/321,255 filed onMar. 9, 1989, now abandoned.

Patients confined to beds for long periods of time must be turnedfrequently to rest on different portions of their bodies in order toavoid the onset of bed sores or to alleviate discomfort associated withsame. Turning the patient also helps avoid accumulation of fluid in thelungs. Heretofore, turning a patient has been a labor intensive task ofthe hospital staff, and the rising cost of hospital staff has made thistask ever more expensive for the hospital and ultimately the patient.

Though not a low air loss bed, one apparatus and method of turning apatient is disclosed in U.S. Pat. No. 3,485,240 to Fountain. Theapparatus has cushions 11, 12, which overlap one another substantiallyso that substantially the patient's entire body may be accommodated byeach pad. Each cushion is normally not inflated when the patient restshorizontally on the bed. Each cushion has a surface that can be inclinedwhen inflated. A mechanism 30 individually inflates and evacuatescushions 11, 12 and includes an outlet switch 31, a timer 32, and afour-way valve 33. In one position, valve 33 connects cushion 11 to avacuum to evacuate same and cushion 12 to a pump to inflate same. In asecond position, cushion 12 is connected to the pump and cushion 11 isconnected to the vacuum. The timer controls the sequence of alternatingbetween the two positions of valve 33. Each cushion can be segmented topermit different segments to be inflatable to a different degree orcontour.

In order to prevent slippage of the patient on the inclined surface ofthe Fountain cushions, the patient is required to be confined by straps41, 42 around the patient's legs for example. This constraint becomesuseless if the patient is an amputee and is detrimental to the healingprocess if the patient has sores or wounds on the legs or other portionsof the body that would be constrained by the straps. Moreover, suchstraps are uncomfortable and interfere with the ability of the patientto repose restfully. Furthermore, the inflation and evacuation mechanism30 does not permit a steady state of partial evacuation of cushions 11,12, requiring instead either total deflation or total inflation duringthe steady state of operation that occurs once inflation and evacuationis complete.

Another apparatus and method for automatically turning a patientconfined to a low air loss bed is disclosed in European Pat. ApplicationPublication No. 0 260 087 A2 to Vrzalik. To eliminate the need forconfinement straps, this apparatus provides a retaining means byspecially configuring the shape of air bags mounted transversely on aframe. In one embodiment, this retaining means takes the form of apillar which is integral with each air bag and which, when inflated,projects upwardly to form the end and corner of the air bag. The meansfor moving the patient toward one side of the frame when thesubstantially rectangular Vrzalik air bag is inflated includes atrapezoidal-shaped cutout in the top of the air bag and disposed betweenthe center of the bag and only one end of the bag. The bags are disposedon the frame so that adjacent bags are disposed with the cutout towardopposite sides of the frame. All the bags with the cutout on one side ofthe frame define a first set of bags, while the bags with the cutout onthe opposite side of the frame define a second set of bags. When thefirst set of bags is inflated while deflating the second set, thepatient is moved to one side of the bed.

The Vrzalik device also includes an air control box that is interposedin the flow of air from a gas source to a plurality of gas manifoldsthat connect to the air bags. The air control box has individuallyadjustable valves for changing the amount of gas delivered to each ofthe gas manifolds. Each of the valves is individually adjustable tochange the amount of flow from the gas source through the air controlbox to each of the gas manifolds. The air control box also has means forheating the gas flowing through it. A heat sensor is disposed in one ofthe gas manifolds and is operable so that the heating means iscontrolled by signals therefrom.

The patient care industry has become sensitive to the patient'spsychological reaction to the environment of life support machinery.Complex machinery such as shown in Vrzalik FIGS. 1 and 6 tends to remindthe patient of the patient's precarious health and the heroic andexpensive technological effort that is required to sustain the patient.Accordingly, it becomes desireable to minimize the visibility ofconnecting tubing and hosing such as shown in Vrzalik FIG. 6 so that thepatient support system more closely resembles the bed in which thepatient sleeps when at home.

A low air loss patient support requires maintenance by both technicalpersonnel and hospital personnel. The cost of providing such maintenanceis directly proportional to the time required to perform suchmaintenance.

OBJECTS AND SUMMARY OF THE INVENTION

It is the principal object of the present invention to provide animproved patient support system comprising a plurality of separatelypressurizable multi-chamber inflatable sacks in which combinations ofadjacent sacks define body support zones that support different regionsof the patient at differing sack pressures.

It is a further principal object of the present invention to provide animproved patient support system and method which permit automaticallyturning a patient from side to side and back to horizontal atpredetermined intervals, even when the patient support is articulated.

Yet another principal object of the present invention is to provide animproved patient support system and method for automatically andperiodically relieving pressure points between the patient and thesupport system, even when the patent support is articulated.

Another principal object of the present invention is to provide animproved low air loss patient support system with a modular constructionand arrangement that facilitates use, repair and maintenance of thesystem.

It also is a principal object of the present invention to provide amulti-chambered inflatable sack that facilitates automatically turning apatient and relieving pressure points on a low air loss patient supportsystem.

A further principal object of the present invention is to provide animproved modular support member that is carried by the articulatableframe of a low air loss patient support system and provides internalpathways for the supply of air to one or more inflatable sacksdetachably connected to the upper surface of the modular support member.

Yet another principal object of the present invention is to provide aquick-disconnect connection fitting for attaching the inflatable sacksof a low air loss patient support system to a modular support membersuch that the sacks can be manually connected and disconnected yetmaintain an air-tight engagement while they are connected.

Still another principal object of the present invention is to provide amodular manifold for distributing pressurized air to the sacks of a lowair loss patient support system through a plurality of pressure controlvalves mounted on the manifold and easily connected thereto anddisconnected therefrom by manual manipulations for ease of maintenanceand servicing.

A still further principal object of the present invention is to providea bi-modal system of supplying pressurized air to the inflatable sacksof a low air loss patient support system.

Additional objects and advantages of the invention will be set forth inpart in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention may be realized and attained bymeans of the instrumentalities and combinations particularly pointed outin the appended claims.

To achieve the objects and in accordance with the purpose of theinvention, as embodied and broadly described herein, the modular low airloss patient support sYstem of the present invention preferably includesa frame that carries the other components of the system. The frame ismounted on castors for ease of movement and preferably has a pluralityof articulatable sections that can be lifted by conventional hydrauliclifting mechanisms and articulated by conventional articulation devices.

In accordance with the present invention, a plurality of elongatedinflatable multi-chamber sacks are disposed transversely across thepatient support system. Each sack preferably has four separately definedchambers, including two opposite end chambers and two intermediatechambers. A separate sack entrance opening is defined through the bottomof each end chamber. Each intermediate chamber preferably is shaped as aright-angle pentahedron and has a diagonal wall that faces the center ofthe sack, and a base wall that preferably forms a common wall with theadjacent end chamber' vertically disposed internal side wall.Preferably, a single web forms the diagonal wall of both intermediatechambers. Because of the shape of the intermediate chambers, one isdisposed predominately to the left side of the patient support, and theother is disposed predominately to the right side of the patientsupport. A restrictive flow passage is defined through the common wallbetween each end chamber and each adjacent intermediate chamber.Preferably, the restrictive flow passage includes a hole defined by agrommet having an opening therethrough and mounted in a web that formsboth the base wall of an intermediate chamber and the verticallydisposed internal side wall of the end chamber adjacent the intermediatechamber. The grommet is sized to ensure that the end chambers havefilling priority over the intermediate chambers. Especially when thepatient is being supported atop the section of the sack which includesthe intermediate chambers, the end chambers fill with air before theintermediate chambers and collapse for want of air after theintermediate chambers.

In still further accordance with the present invention, means areprovided for supplying air to each sack. The means for supplying air toeach sack preferably includes a blower electrically powered by a motorso that the blower can supply pressurized air to the sacks at pressuresas high as thirty inches of standard water.

The means for supplying air to each sack further preferably includes asupport member carried by the frame. The support member preferably isrigid to provide a rigid carrier on which to dispose the sacks and maycomprise a plurality of separate non-integral sections so that aone-to-one correspondence exists between each support member section andeach articulatable section of the frame. Each section of the rigidsupport member preferably comprises a modular support member thatdefines a multi-layered plate which has an upper layer, a lower layerand a middle layer between the other two. The three-layered plate has atop surface, a bottom surface, two opposed ends, and two opposed sideedges. A plurality of inlet openings are defined through at least one ofthe side edges. In appropriate embodiments, a plurality of exit openingsare defined in the opposite side edge. For example, the plate at eachend of the patient support only has inlet openings defined through oneof the side edges. A plurality of air sack supply openings are definedthrough the plate from the top surface and preferably extend completelythrough the three layers of the plate. In at least one of the plates,preferably the seat plate, a plurality of pressure control valveopenings are defined through the bottom surface of the plate. Aplurality of channels preferably are defined and enclosed between thetop surface and the bottom surface of the plate and connect the variousinlet openings, outlet openings, air sack supply openings, and pressurecontrol valve openings to achieve the desired configuration of airsupply to each of the sacks disposed atop the top surface of the plate.

In yet further accordance with the present invention, the means forsupplying gas to the sacks also preferably includes a hand-detachableairtight connection comprising one component secured to the air sack anda second component secured to the modular support member. The forcerequired to connect and disconnect these components is low enough topermit these operations to be accomplished manually by hospital staffwithout difficulty. Both components preferably are formed of a resilientplastic material. One of the components comprises an elongated femaleconnection fitting that has an exterior configured to airtightly engagean air sack supply opening defined through the modular support member. Alocking nut screws onto one end of the fitting, which extends throughthe bottom plate, and secures the fitting to the air sack supply openingof the modular support member. The fitting preferably has an axiallydisposed cylindrical coupling opening with a fitting groove definedcompletely around the interior thereof and near one end of thecylindrical coupling opening. A resiliently deformable flexible O-ringis held within the fitting groove. A channel opening is defined throughthe coupling cylinder in a direction normal to the axis of the couplingcylinder and is disposed to be aligned with the support member channelthat connects to the air sack supply opening which engages the fitting.A spring-loaded poppet is disposed in the cylindrical coupling openingand is biased to seal the coupling opening.

The other component of the connection includes an elongated couplingthat is secured at one end to the air entrance opening of the sack andextends outwardly therefrom. The coupling has an axially defined openingthat permits air to pass through it and into the sack. The exterior ofthe coupling is configured to be received within the interior of theconnection fitting's cylindrical coupling opening. Insertion of thecoupling into the interior of the fitting depresses the poppetsufficiently to connect the channel opening with the axially definedopening of the coupling. The coupling's exterior surface defines agroove that is configured to receive and seal around the deformable0-ring of the connection fitting therein when the coupling is insertedinto the connection fitting. The 0-ring seals and provides a mechanicallocking force that holds the coupling in airtight engagement with thefitting.

The coupling preferably is secured to extend from the air entranceopening of the air sack with the aid of a grommet and a retaining ring.The grommet preferably is heat sealed to the fabric of the air sack onthe interior surface of the air sack around the air entrance opening.The coupling extends through the grommet and the air entrance opening. Apull tab is fitted over the coupling and rests against the exteriorsurface of the air sack. A retaining ring is passed over the couplingand mechanically locks against the coupling in air-tight engagement withthe air sack. The pull tab can be grasped by the hand of a person whodesires to disconnect the coupling from the fitting. In this way, thematerial of the air sack need not be pulled during disconnection of thecoupling from the fitting. This prevents tearing of the air sack nearthe air entrance opening during the disconnection of the coupling fromthe fitting.

In still further accordance with the present invention, the means forsupplying air to each of the sacks further preferably includes a modularmanifold for distributing air from the blower to the sacks. The modularmanifold preferably provides means for mounting at least two pressurecontrol valves thereon and for connecting these valves to a source ofpressurized air and to an electric power source. As embodied herein, themodular manifold preferably includes a log manifold that has anelongated body defining a hollow chamber within same. A supply hose isconnected to the main body and carries pressurized air from the blowerto the hollow chamber of the main body. End walls are defined at thenarrow ends of the main body and contain a conventional pressure checkvalve therein to permit technicians to measure the pressure inside thehollow chamber of the main body.

One section of the main body defines a mounting wall on which aplurality of pressure control valves can be mounted by inserting theirvalve stems into one of a plurality of ports defined through themounting wall and spaced sufficiently apart from one another to permitside-by-side mounting of the valves. Each port has a bushing mountedtherein to engage one or more 0-rings on the valve stem of each valve.This renders each valve easily insertable and removable from the logmanifold.

The log manifold further preferably includes a circuit board thatpreferably is mounted to the exterior of the main body adjacent themounting wall and includes electronic circuitry for transmittingelectronic signals between a microprocessor and the valves mounted onthe log manifold. A plurality of electrical connection fittings aredisposed on the circuit board, and each fitting is positioned inconvenient registry with one of the ports defined through the mountingwall. These electrical connection fittings are provided to receive anelectrical connector of each pressure control valve. One or more fusesare provided on the circuit board to protect it and the componentsattached to it. Preferably, the fuses are mounted on the exterior of thelog manifold to provide technicians with relatively unobstructed accessto them to facilitate troubleshooting and fuse replacement.

In further accordance with the present invention, means are provided formaintaining a predetermined pressure in the sacks. As embodied herein,the means for maintaining a predetermined pressure in the sackspreferably includes a pressure control valve. In a preferred embodiment,a plurality of pressure control valves are provided, and each pressurecontrol valve controls the pressure to more than one sack or more thanone chamber of a sack. As embodied herein, each pressure control valveincludes a housing having an inlet defined through one end and an outletdefined through an opposite end. An elongated valve passage is definedwithin the housing and preferably is disposed in axial alignment withthe inlet. The longitudinal axis of the passage preferably is disposedperpendicularly with respect to the axis of the valve outlet which isconnected to the passage. The housing further defines a chamber disposedbetween the inlet and a first end of the valve passage and preferably iscylindrical with the axis of the cylinder disposed perpendicularly withrespect to the axis of the passage. The valve further preferablyincludes a piston that is disposed within the chamber and preferablyrotatably displaceable therein to vary the degree of communicationthrough the chamber that is permitted between the valve inlet and thevalve passage. The valve further includes an electric motor that ismounted outside the housing and near the chamber. The motor is connectedto the piston via a connecting shaft that has one end non-rotatablysecured to the rotatable shaft of the motor and an opposite endnon-rotatably connected to the piston, which also is cylindrical inshape. The piston has a slot extending radially into the center of thepiston so that depending upon the position of this slot relative to theinlet and the passage, more or less air flow is permitted to passthrough the holes between the inlet and the passage. Accordingly, theposition of the piston within the chamber determines the degree ofcommunication that is permitted through the chamber and thus the degreeof communication permitted between the valve passage and the valveinlet. This degree of communication effectively regulates the pressureof the air flowing through the valve. Preferably, the piston slot isconfigured so as to provide a linear change in pressure as the piston isrotated.

The pressure control valve further preferably includes a pressuretransducer that communicates with the valve passage to sense thepressure therein. The pressure transducer converts the pressure sensedin the valve passage into an electrical signal that is transmitted to anelectronic circuit mounted on a circuit card of the valve. The circuitcard receives the electrical signal transmitted from the transducercorresponding to the pressure being sensed in the valve passage. Thecircuit card has a comparator circuit that compares the signal from thetransducer to a reference voltage signal received from a microprocessorvia the circuit board of the log manifold. The valve circuit controlsthe valve motor according to the result of the comparison of thesesignals received from the microprocessor and transducer to open or closethe valve to increase or decrease the pressure. The control valve has anelectrical lead that is connected to the valve circuit card andterminates in a plug that can be connected to the electrical connectionfitting on the log manifold.

A dump outlet hole is defined through the valve housing in the vicinityof the valve chamber. A dump passage is also defined through the valvepiston and is configured to connect the dump hole to the valve passageupon displacement of the piston such that the dump hole becomes alignedwith the dump passage of the piston. When the dump hole becomes alignedwith the dump passage of the piston, the valve inlet becomes completelyblocked off from any communication with the valve passage. Upon suitableoperator control of the microprocessor, the dump hole becomes connectedto the valve passage via the dump passage of the piston to permit theescape of air from the sacks to the atmosphere in a rapid deflationcycle.

A conventional pressure check valve is mounted in a manual pressurecheck opening defined through the housing of the pressure control valve.This permits the pressure inside the pressure control valve to bemanually checked for purposes of calibrating the pressure transducer forexample.

The means for maintaining a predetermined pressure preferably furtherincludes a programmable microprocessor, which preferably ispreprogrammed to operate the pressure control valves and the blower topressurize the sacks at particular reference pressures. Themicroprocessor calculates each sack reference pressure according to theheight and weight of the patient, and the portion of the patient beingsupported by the sacks connected to the respective pressure controlvalve. For example, the sacks supporting the head and chest of thepatient may require a different pressure than the sacks supporting thefeet of the patient. The pressures also differ depending upon whetherthe patient is lying on his/her side or back. A control panel isprovided to enable the operator to provide this information to themicroprocessor, which is programmed to calculate a separate referencepressure for each mode of operation of the patient support for eachpressure control valve. The microprocessor uses an algorithm to performthe calculation of the sack reference pressure, and this algorithm hasconstants which change according to the elevation of the patient, thesection of the patient being supported, and whether the patient is lyingon the patient's side or the patient's back.

The output of blower 66 preferably is controlled by a blower controlcircuit which receives a control voltage signal from the microprocessor.A pressure transducer measures the pressure preferably at the outlet ofthe blower, and this measured pressure is supplied to the microprocessorwhich stores it in one of its memories. This memory is not continuouslyupdated, but rather is updated once every predetermined interval of timein order to filter out brief transient pressure changes in the measuredpressure so that such transients do not affect control over the blower.The microprocessor uses the highest pressure in the sacks to calculate areference pressure for the blower that is 3 to 4 inches of standardwater higher than the highest sack pressure. The microprocessor ispreprogrammed to compare the reference pressure with the measuredpressure. If this comparison has a discrepancy greater than apredetermined discrepancy of about one inch of standard water, then themicroprocessor changes the control voltage provided to the blowercontrol circuit so as to reduce this discrepancy.

The sacks of the support system are divided into separate body zonescorresponding to a different portion of the patient's body requiring adifferent level of pressure to support same. Each body zone iscontrolled by two pressure control valves in one operational mode, onefor the chambers on one side of the sacks and one for the chambers onthe other side of the sacks. In another operational mode, the twopressure control valves are connected so that each pressure controlvalve controls the pressurization of the chambers in both sides of everyalternate sack in the body zone. The microprocessor is preprogrammed tocalculate an optimum reference pressure for supporting the patient ineach body zone. This reference pressure is determined at the valvepassage where the pressure transducer of each pressure control valve issensing the pressure. This reference pressure is calculated based uponthe height and weight of the patient. Once this reference pressure hasbeen calculated for the particular patient and for the particular modeof operation of the patient support system, for example, turning mode ata particular attitude, pulsation mode at a particular level ofdepressurization, standard operating mode, etc., the microprocessorsignals the circuit board which transmits this signal to the circuitcard of the pressure control valve. The circuit card of the valvecompares the pressure being measured by the transducer in each valvepassage with the reference pressure which the microprocessor hascalculated for the particular conditions of operation. Depending uponwhether the measured pressure is greater than or lower than thecalculated reference pressure, the circuit card signals the valve'smotor to open or close the valve to increase or decrease the pressure toarrive at the target reference pressure. The circuit card continuouslymonitors this comparison and controls the valves accordingly.

The microprocessor preferably has parallel processing capability and isconnected electrically to the circuit board of the log manifold via aribbon cable electrical connector. The parallel processing capability ofthe microprocessor enables it to monitor and control all of the pressurecontrol valves simultaneously, as opposed to serially. This increasesthe responsiveness of the pressure controls to patient movements in thesupport system.

In still further accordance with the present invention, there isprovided means for switching between different modes of pressurizing thesacks. As embodied herein, the mode switching means preferably includesat least one flow diverter valve. The number of flow diverter valvesdepends upon the number of different pressure zones desired for thepatent support system. Each pressure zone, also known as a body zone,includes one or more sacks or sack chambers which are to be maintainedwith the same pressure characteristics. In some instances for example,it is desired to have opposite sides of the sack maintained at differentpressures. In other instances for example, it becomes desireable to havethe pressure in every other sack alternately increasing together for apredetermined time interval and then decreasing together for apredetermined time interval.

Each flow diverter valve preferably is mounted within a modular supportmember and includes a first flow pathway and a second flow pathway. Theends of each flow pathway are configured to connect with the ends of twoseparate pairs of channels defined in the modular support member. Theflow pathways are mounted on a rotating disk that can be rotated tochange the channels to which the ends of the two flow pathways areconnected. This changes the flow configuration of the path leading fromthe blower to the individual sacks and sack chambers. At one position ofthe rotating disk, all of the chambers on one side of the sacks of abody zone are connected to the blower via one pressure control valve andall of the other sides of the sacks in the body zone are connected tothe blower via a second pressure control valve. In a second position ofthe rotating disk, every alternate sack in the body zone has itschambers on both sides connected to one pressure control valve, andevery other alternate sack in the body zone has both of its chambersconnected to the blower via a second pressure control valve. Switchingbetween the two positions of the rotating disk changes the flowconfiguration from the blower to the individual chambers of the sacks.This enables the present invention to be operated in two distinctlydifferent modes of operation with a minimum number of valves andconnecting pathways.

The phrase "pressure profile" is used herein to describe the range ofpressures in the sacks of the patient support system at any givensupport condition. The pressure in the sacks in one body zone of thesupport system likely will be different from the pressure in the sacksof another body zone because the different weight of different portionsof the patient's body imposes a corresponding different supportrequirement for each particular body zone. If the individual pressuresin the sacks of all of the body zones were to be represented on a bargraph as a function of the linear position of the sacks along the lengthof the patient support, a line connecting the tops of the bars in thegraph would depict a certain profile. Hence, the use of the term"pressure profile" to describe the pressure conditions in all of thesacks at a given moment in time, either when the pressures are changingor in a steady state condition.

In accordance with one of the methods of the present invention madepossible by the support system of the present invention, the patient canbe automatically tilted from side-to-side in a predetermined sequence oftime intervals. The method of turning or tilting the patient includesthe step of configuring the flow pathway from the blower to the sacks ineach body zone such that the two chambers in one side of each of thesacks are controlled by one pressure control valve, and the two chambersin the other side of each of the sacks are controlled by anotherpressure control valve.

The step of separately controlling the air pressure that is supplied toeach side of each of the sacks in each body zone preferably isaccomplished by correctly configuring the flow diverter valve. The nextstep in tilting or turning the patient involves lowering the pressure inthe side of the sacks to which the patient is to be tilted. The pressuremust be lowered from a first pressure profile, which previously wasestablished to support the patient in a horizontal position, to apredetermined second pressure profile which depends upon the height andweight of the patient and the angle to which the patient is to betilted. The next step in the method of tilting or turning the patientrequires raising the pressure in the side of the sacks that is oppositethe side to which the patient is being tilted. This requires raising thepressure in the non-tilted side of each of the sacks to a predeterminedthird pressure profile. This raised pressure compensates for the lowerpressure profile in the tilted side of the sacks. Thus, the overallpressure being supplied to support the patient remains sufficient tosupport the patient in the tilted position.

Preferably the steps of lowering the pressure in one side of the sacksoccurs in conjunction with and at the same time as the step of raisingthe pressure in the other sides of the sacks. The changes in pressureare effected under the control of the microprocessor which calculatesthe desired reference pressure for the tilted condition based upon theheight and weight of the patient and transmits a corresponding referencevoltage signal to the circuit card of the pressure control valve whichcloses the valve opening until the desired pressure has been attained,as signaled by the pressure transducer monitoring each pressure controlvalve. The microprocessor can be programmed to maintain the patient inthe tilted position for a predetermined length of time. At the end ofthis time, the microprocessor can be programmed to return the patientgradually to the horizontal position by reversing the procedure used totilt the patient. In other words, the pressure is increased to the sideof the sacks to which the patient has been tilted, and decreased for theother side of the sacks until both sides of the sacks attain the firstpredetermined pressure profile.

The method of tilting or turning the patient also includes the step ofrestraining the patient from slipping off of the sacks while in thetilted condition. This is accomplished by the unique construction of themulti-chambered sacks and the manner in which the sacks aredepressurized and deflated. The grommet which defines the holeconnecting each intermediate chamber with each end chamber plays aparticularly important role in the ability of each sack to restrain thepatient from slipping off of the sack during tilting. As the pressurecontrol valve controlling the side of the sack to which the patient isto be tilted begins to close, it reduces the pressure being supplied tothis side of these sacks. Thus, the pressure being supplied to the endchamber and the intermediate chamber connected thereto via the flowrestriction passage defined through the grommet are both being reducedin pressure. Recall that the microprocessor presets the pressure in thesack depending upon the height and weight of the patient. Once thepressure is reduced from that preset pressure, the weight of the patientabove the intermediate chamber begins to squeeze the air from theintermediate chamber through the grommet and into the end chamber. Thisreduction in pressure results in the deflation of the intermediatechamber while the end chamber continues to remain fully inflated, thoughat the same reduced pressure as the connected intermediate chamber.Since the end chamber remains inflated, it remains vertically disposedat the end of the sack, and as such the inflated end chamber acts as aconstraint that prevents the patient from rolling past the end chamberand slipping off the sacks of the patient support.

In further accordance with the present invention, a method is providedfor using the patient support system of the invention to providepressure point relief between the sacks and the patient by operating thepatient support in a pulsation mode of operation. As embodied herein,the method for providing pressure point relief preferably includes thestep of configuring the patient support system so that in each bodyzone, every alternate sack is pressurized via one pressure control valveand every other alternate sack is pressurized via a second pressurecontrol valve. This step preferably is accomplished by configuring theflow diverter valve to reconfigure the flow path to connect every otheradjacent sack in each zone to a separate pressure control valve. Thenext step of the method includes supplying air pressure at a firstpressure profile to the sacks connected to one of the pressure controlvalves and supplying the sacks connected to the other pressure controlvalve at the same first pressure profile.

The method for pulsating the pressure in the sacks further includes thestep of decreasing the pressure being supplied to the sacks through oneof the pressure control valves during a first interval of time. Thepressure is decreased until a predetermined second pressure profile isbeing provided to the sacks in this first group, which includes everyalternate sack.

The method of pulsating the pressure in the sacks also includes the stepof increasing the pressure being supplied to the sacks through the otherof the pressure control valves during the same first interval of time.The pressure is increased until a predetermined third pressure profileis being provided to the sacks in this second group, which includes theother set of alternating sacks. Preferably, the third pressure profileis determined so that the average of the second and third pressureprofiles equals the first pressure profile.

The method for pulsating the pressure in the sacks next includes thestep of maintaining the first group of alternating sacks at the secondpressure profile while maintaining the sacks in the second group ofalternating sacks at the third pressure profile. This maintenance stepoccurs over a second interval of time.

The method for pulsating the pressure in the sacks next includes thestep of increasing the pressure in the first group of alternating sacksuntil the third pressure profile is attained while decreasing thepressure being supplied to the sacks in the second group of alternatingsacks until the second pressure profile is attained for the second groupof alternating sacks. Thus, the pressure profiles of the two groups ofalternating sacks are reversed during a third interval of time.

Finally, the method of pulsating the pressure in the sacks includes thestep of maintaining the sacks in the first group of alternating sacks atthe third pressure profile while maintaining the sacks in the secondgroup of alternating sacks at the second pressure profile. Thismaintenance step of the method occurs during a fourth interval of time.This completes one full cycle of pulsation, and this can be repeated aslong as the repetition is deemed to be therapeutic.

Preferably, the time intervals are equal. However, the intervals of timecan be selected as desired. For example, the first and third intervalsof time during which the pressure is changing in the sacks can beselected to be equal and very short. The second and fourth intervals oftime during which the two groups of alternating sacks are maintained atdifferent pressure profiles can also be selected to be equal and can belonger periods of time than the first and third intervals. It also ispossible to choose long periods of time for the first and thirdintervals and short periods of time for the second and fourth intervals.

The accompanying drawings which are incorporated in and constitute apart of this specification, illustrate one embodiment of the inventionand, together with the description, serve to explain the principles ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a preferred embodiment of the presentinvention;

FIG. 2 shows a cut-away perspective view of a preferred embodiment ofcomponents of the present invention;

FIG. 3 illustrates a partial perspective view of a portion of acomponent of an embodiment of the present invention;

FIG. 4 illustrates a partial perspective view of components of anembodiment of the present invention;

FIG. 5 illustrates a partial cross-sectional view with the viewer's lineof sight taken generally along the lines 5--5 of FIG. 4;

FIG. 6 illustrates perspective assembly view of embodiments,,ofcomponents of the present invention;

FIG. 7 illustrates a cut-away perspective view of an embodiment of acomponent of the present invention;

FIG. 8 illustrates a cut-away side view of the component like the oneshown in FIG. 7;

FIG. 9a-9d illustrate different views of a preferred embodiment of acomponent of a device suitable for use in the present invention;

FIG. 10 illustrates a perspective view of components of an embodiment ofthe present invention;

FIG. 11 illustrates a schematic view of components of an embodiment ofthe present invention;

FIG. 12 shows a schematic view of components of an embodiment of thepresent invention;

FIG. 13 illustrates a schematic view of a components of an embodiment ofthe present invention;

FIG. 14 illustrates a cut-away perspective view of a component of, thepresent invention as if it were taken along the lines 14--14 in FIG. 13;

FIG. 15 illustrates a component used in an embodiment of the invention;and

FIG. 16 illustrates an embodiment of a component of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference now will be made in detail to the present preferredembodiments of the present invention, examples of which are illustratedin the accompanying drawings. As used herein, air tightly is a relativephrase that refers to essentially no air leakage at the operating airpressures of the present invention.

The preferred embodiment of the modular low air loss patient supportsystem is shown in FIG. 1 and is generally designated by the numeral 20.

The patient support system of the present invention preferably includesa frame, indicated generally in FIG. 1 by the numeral 30, having atleast one articulatable section 32. The frame carries the components ofthe patient support system and typically has more than one articulatablesection and preferably is mounted on castors for ease of movement in thehospital environment. The hydraulic lifting mechanisms for raising andlowering portions of the frame, including the articulatable sections ofthe frame, are conventional, and suitable ones are available fromHillenbrand Industries of Batesville, Indiana, sold under the Hill-Rombrand.

In accordance with the present invention, a plurality, preferablyseventeen in the illustrated embodiment (FIGS. 12 and 13), of elongatedinflatable sacks are provided. As shown in FIG. 2 for example, each ofthe sacks 34 of the present invention preferably has a multi-chamberinternal configuration, and preferably four chambers are provided. Inone embodiment shown in the drawings, the shape of each inflated sack isgenerally rectangular and preferably has exterior dimensions thirty-twoinches long, ten and one-half inches high, and four and one-half inchesthick. The patient support surface of each sack is provided by a top 36which measures four and one-half inches by thirty-two inches, and abottom 38 (FIG. 3) is similarly dimensioned. Depending upon theirlocation on the patient support, the sack may include a plurality of pinholes (not shown) to allow a small amount of air to bleed from the sack.The diameters of the holes preferably are about fifty thousandths of aninch, but can be in the range of between eighteen to ninety thousandthsof an inch. Each exterior end 40 of each sack measures ten and one-halfinches by four and one-half inches, and each exterior side 42 measuresten and one-half inches by thirty-two inches. Each sack is preferablyintegrally formed of the same material, which should be gas-tight andcapable of being heat sealed. The sacks preferably are formed of twillwoven nylon which is coated with urethane on the surfaces forming theinterior of the sack. The thickness of the urethane coating is in therange of three ten thousandths of an inch to two thousandths of an inch.Vinyl or nylon coated with vinyl also would be a suitable material forthe sack. Unless the sacks are designed to be disposable, the materialshould be capable of being laundered.

Internally, the sack preferably is configured with four separatelydefined chambers. As shown in FIG. 2 for example, the internal webs 44of each sack preferably are integral with the outside walls of eachsack, and are at least joined in airtight engagement therewith. An endchamber 46 is disposed at an opposite end of each sack. Each end chamberis generally rectangular in shape with one of the narrow ends 48 formedby a portion of the top of the sack, and the opposite narrow end 50formed by a portion of the bottom of the sack. As shown in FIG. 5 forexample, the narrow end of each end chamber forming a section of thesack bottom is provided with a sack air entrance opening 52 through thebottom of the sack.

As shown in FIG. 2 for example, each multi-chamber sack includes a pairof intermediate chambers 54 disposed between the end chambers. Eachintermediate chamber preferably is shaped as a right-angle pentahedron.Each intermediate chamber 54 has a base wall 56, an altitude wall 58, adiagonal wall 60, and two opposite triangular-shaped side walls 62. Eachbase wall, altitude wall, and diagonal wall has a generally rectangularshaped perimeter. Each base wall 56 is connected at a right angle toeach altitude wall 58. Each diagonal wall 60 is connected at one edge toeach base wall and at an opposite edge to the altitude wall. The edgesof each triangular side wall are connected to oppositely disposed edgesof the base, altitude, and diagonal walls. As shown in FIG. 2 forexample, each intermediate chamber is disposed within each sack so thatits diagonal wall faces toward the center of the sack and toward theother intermediate chamber. One of the intermediate chambers is disposedabove the other intermediate chamber so that it becomes convenientlyreferred to as the upper intermediate chamber, while the otherintermediate chamber becomes the lower intermediate chamber. Thealtitude wall of the upper intermediate chamber preferably is formed bya middle section of the top 36 of the sack 34. The altitude wall of thelower intermediate chamber preferably is formed by the middle section ofthe bottom 38 of the sack 34.

As shown in FIG. 1 for example, each sack preferably is disposed toextend transversely across the longitudinal centerline of the patientsupport, and the intermediate chambers are disposed in the center ofeach sack. Thus, the intermediate chambers also are disposed to extendtransversely across the longitudinal centerline of the patient support.As shown in FIG. 2 for example, one of the intermediate chambers isdisposed at least partly above the other intermediate chamber andpreferably is disposed completely above the other intermediate chamber.Because of the symmetrical position of each sack relative to thelongitudinal centerline of the patient support system, one of theintermediate chambers is disposed predominately to the left side of thecenterline and has a minority portion disposed to the right side of thecenterline. Similarly, the other of the intermediate chambers isdisposed predominately to the right side of the longitudinal centerlineof the patient support and has a minority portion disposed to the leftof the centerline.

Each sack has a pair of restrictive flow passages, one connecting eachof the end chambers to the adjacent intermediate chamber. As shown inFIG. 2 for example, preferably a single web serves as a common wall ofan end chamber and the base wall of the adjacent intermediate chamber.As shown in FIG. 2 for example, each restrictive flow passage can bedefined by a hole 64 through the web that is common to the intermediatechamber and the adjacent end chamber. Hole 64 preferably is defined by agrommet having an opening therethrough and mounted in a web that formsboth the base wall of an intermediate chamber and the verticallydisposed internal side wall of the end chamber adjacent the intermediatechamber. The grommet is sized to ensure that the end chambers havefilling priority over the intermediate chambers and thus are the firstpriority over with air and the last to collapse for want of air. Forsacks dimensioned as described above for example, a grommet having a 1/4inch diameter opening has been suitable for achieving the desiredfilling and emptying priority.

In further accordance with the present invention, means are provided forsupplying gas, preferably air, to each sack of the patient supportsystem of the present invention. As embodied herein and shownschematically in FIG. 12 for example, the means for supplying air toeach sack preferably includes a blower 66 powered electrically by amotor which runs on a low direct current voltage such as 24 volts. Theblower must be capable of supplying pressurized air to the sacks atpressures as high as 30 inches of standard water but should be capableof supplying pressures in a preferred range of 0 to 18 inches ofstandard water while operating in the blower's optimum performancerange.

As shown in FIG. 12 for example, a pressure transducer 246 measures thepressure at the blower outlet. The measured pressure signal istransmitted to a microprocessor (described hereafter) via a blowercontrol circuit 67 and a circuit board 150 (described hereafter). Blower66 preferably is controlled by voltages supplied by a blower controlcircuit 67 which receives a control voltage signal from themicroprocessor via a circuit board 150. The microprocessor ispreprogrammed to compare the pressure signal received from pressuretransducer 246 to a desired pressure signal calculated by themicroprocessor. Depending upon the result of the comparison, themicroprocessor regulates the power supply to the blower control circuit.However, the methodology used by the microprocessor to compare thecalculated pressure to the measured pressure contains a built-in delay(preferably about three seconds) so that the response to changes in themeasured blower pressure is not instantaneous. The deliberate time delayin the response to the measured blower pressure assures control loopstability and prevents unwarranted pressure fluctuations in the sacks.Otherwise, instantaneous real time pressure corrections in response tothe blower output pressure and control valve output pressure could causepressure oscillations in the system.

As embodied herein and shown in FIGS. 4, 5, and 14, and schematically inFIGS. 12 and 13, the means for supplying air to each sack preferablyfurther includes a support member carried by the frame. The supportmember preferably is rigid to provide a rigid carrier on which todispose sacks 34 and may comprise a plurality of separate non-integralsections so that a one-to-one correspondence exists between each supportmember section and each articulatable section of the frame. As shown inFIG. 14 for example, each section of the rigid support member preferablycomprises a modular support member 68 and defines a multi-layered plate70. Each plate 70 preferably is thin and has a flat top surface 72 andan opposite bottom surface, which also preferably is flat. As shown inFIG. 14 for example, each plate has an upper layer 74, a lower layer 76,and a middle layer 78 disposed between the upper and lower layers. Asshown partially in FIG. 4 for example, the three layers are sealedaround the edges to form two opposed ends 80 and two opposed side edges82 joining between the ends.

As shown in FIGS. 4 and 13 for example, a plurality of inlet openings 84are defined through at least one of the side edges 82. As shown in FIG.13 for example, depending upon the relative position of the modularsupport member, some of the modular support members have a plurality ofoutlet openings 86 defined in an opposite side edge 82. The modularsupport manifold of Zone IV for example also has a plurality of outletopenings 86 defined through the other of the side edges, while themodular support manifold of Zone V only has inlet openings 84 definedthrough one of the side edges 82, and lacks outlet openings on theopposite side edge. As partially shown in FIG. 4 for example, the inletopenings 84 of one plate 70 are engaged by fittings 88 and flexiblehoses 90 to become connected to the outlet openings 86 of an adjacentmodular support member.

As shown in FIGS. 5 and 14, and schematically in FIG. 13, for example,the upper layer defines a plurality of air sack supply openings 92 whichextend through the top surface of each plate 70, and preferably throughall three layers of plate 70. As shown in FIG. 5 for example, these airsack supply openings 92 are used to hold a special connection fitting(described hereafter) that connects the air sacks to a supply ofcontrolled pressurized air.

As shown schematically in FIG. 13 for example, at least one of themodular support members defines a seat sack support member 94 (Zone III)and includes a plurality of pressure control valve openings 96 definedthrough the lower layer 76 and extending through the bottom surface ofthe plate 70. Each pressure control valve opening 96 is configured to beconnected to a pressure control valve (described hereinafter). Each ofthe ten pressure control valve openings 96 shown in FIG. 13 isschematically represented by a circle inscribed within a box. To avoidunnecessarily cluttering FIG. 13, only three of the pressure controlopenings are provided with designating numerals 96. Preferably, one endof a rigid elbow 98 (FIGS. 7 and 8) has a flexible bellows (not shown)which is connected to each pressure control valve opening 96, and theother end of the elbow is connected to the output end of the pressurecontrol valve. The seat sack support member preferably includes at leastone pressure control valve opening for each pressure control valverequired by the particular configuration of the patient support system.Each pressure control valve opening intersects with a channel (describedhereafter) for supplying air to the air sacks.

As shown in FIGS. 5 and 14, and schematically in FIGS. 11-13, forexample, the layers of each plate 70 preferably combine to define aplurality of separated enclosed channels therethrough. In an alternativeembodiment, the channels can be formed by discrete flexible tubes. Thechannels are airtight and perform the function of conduits for thetransport of pressurized air from the source of pressurized air to theair sacks. The multi-layer construction of plate 70 allows some channelsto cross one another without intersecting, if the air flow configurationrequires same. As shown schematically in FIG. 13 for example, somechannels 100 connect one of the inlet openings 84 of plate 70 to one ofthe outlet openings 86 defined through the opposite side edge 82 of theplate 70. Some of the channels 102 connect one of the inlet openings 84defined through one of the side edges 82 to one or more of the sacksupply openings 92 defined through the top surface of the plate 70 ofthe modular support member. Each air sack supply opening 92 communicateswith at least one of the channels. Other channels 104 include one of thepressure control valve openings 96.

As embodied herein and shown in FIGS. 2, 3 and 5 for example, the meansfor supplying gas to the sacks preferably includes a hand-detachableairtight connection, an embodiment of same being designated generally inFIG. 5 by the numeral 106. The connection comprises two components, onesecured to the air sack 34, and the other secured to the modular supportmember 70. The force required to insert one of the components into theother component and to disconnect the components from one another is lowenough to permit these operations to be accomplished manually byhospital staff without difficulty. Accordingly, both components of thehand-detachable connection 106 preferably are formed of a semi-rigidplastic material with an elastic 0-ring 114 secured within the interiorof a female connection fitting 108.

As shown in FIG. 5 for example, the component secured to the modularsupport member comprises an elongated female connection fitting 108having an exterior configured to engage airtightly with the air sacksupply opening 92 defined through the plate 70. A plenum 93 is definedbetween the exterior of fitting 108 and air sack supply opening 92. Alower end of the connection fitting extends through the air sack supplyopening 92, and a locking nut 95 screws onto this end of the fitting tosecure same within the air sack supply opening of the modular supportmember.

The female connection fitting 108 has an interior configured with ahollow axially disposed coupling opening 110, preferably a cylinder, toreceive a coupling in airtight engagement therewith. A cylindricalpoppet 97 is disposed in the cylindrical coupling opening and isconfigured to slide within the cylindrical coupling opening. Poppet 97is closed at one end, and a spring rests between the bottom 113 of theinterior of fitting 108 and the interior of the closed end of poppet 97.The spring-loaded poppet is thereby biased to seal off the entrance 111of coupling opening 110.

The connection fitting further defines a fitting groove 112 completelyaround the interior of the fitting and preferably near the entrance 111of coupling opening 110. The connection fitting also includes aresiliently deformable flexible 0-ring 114 held in the fitting groove112. As shown in FIG. 5 for example, the coupling cylinder 110 definedin the interior of the connection fitting further includes a channelopening 116 defined therethrough and in a direction normal to the axisof the coupling cylinder 110. Because of plenum 93, the connectionfitting is always disposed in the air sack supply opening 92 so that thechannel opening 116 communicates with the channel 102 that connects tothe air sack supply opening 92.

As shown in FIGS. 2, 3, 5, and 6 for example, the other component of thehand-detachable connection includes an elongated coupling 118 that issecured at one end to the air entrance opening 52 of the sack andextends outwardly from the sack. The coupling has an axial opening 120defined therethrough to permit air to pass through same and between theinterior and exterior of the sack. The exterior of coupling 118 isconfigured to be received within the interior of the connection fitting.The exterior of the coupling has a groove 122 therearound that isconfigured to seat around and seal against the deformable 0-ring 114 ofthe connection fitting 108 therein when the coupling is inserted intothe connection fitting in airtight engagement with the fitting. Groove122 provides a locking detent to mechanically lock and seal 0-ring 114therein.

As shown in FIG. 6 for example, the coupling is secured to extend fromthe air entrance opening 52 of the air sack with the aid of a grommet126 and a retaining ring 125. The grommet 126 is heat sealed to thefabric of the air sack on the interior surface of the air sack aroundthe air entrance opening. The coupling extends through the grommet 126and the air entrance opening. A pull tab 124 is fitted over the couplingand rests against the exterior surface of the air sack. Alternativeembodiments of pull 124 are shown in FIGS. 3 and 6 for example. Aretaining ring 127 is passed over the coupling and mechanically locksagainst the coupling in air-tight engagement with the air sack. The pulltab 124, which is sandwiched between retaining ring 127 and the sack,can be grasped by the hand of a person who desires to disconnect thecoupling from the fitting. In this way, the material of the air sackneed not be pulled during disconnection of the coupling from thefitting. This prevents tearing of the air sack near the air entranceopening during the disconnection of the coupling from the fitting.

As shown in FIG. 5 for example, connection fitting 108 preferablyincludes a poppet 97 that is a spring loaded cylindrical member disposedconcentrically within coupling cylinder 110 so that one end of thespring 99 rests against the closed end of the poppet, and the other endof the spring rests against the bottom 113 of the interior of connectionfitting 108. Thus, when coupling 118 is inserted into coupling cylinder110, coupling 118 depresses poppet 97 and connects channel opening 116to axial opening 120 of coupling 118. When no coupling 118 is insertedinto coupling cylinder 110, the spring forces the poppet to seal against0-ring 114 and thereby seal the coupling cylinder opening 110 at theentrance 111 thereof near the top layer 74 of plate 70. This permits onesack to be detached while air is being supplied to the others withoutleakage of air through the coupling cylinder opening 110. The sealingeffect of the poppet also prevents fluids from entering the channels ofplate 70, and this is advantageous during cleaning of the upper surfacesof plate 70.

In keeping with the modular configuration of the patient support systemof the present invention, the means for supplying air to each sackfurther preferably includes a modular manifold for distributing air fromthe blower to the sacks plugged into the modular sack support member.The modular manifold provides means for mounting at least two pressurecontrol valves and for connecting same to a source of pressurized airand to an electric power source. Because its elongated shape resembles a"log," such modular manifold is sometimes referred to as the logmanifold, and one embodiment is designated by the numeral 128 in FIG. 10for example. Log manifold 128 includes an elongated main body 130 thatis hollow and defines a hollow chamber 132 within same. As shown in FIG.10 for example, main body 130 is shaped as a long rectangular tube whichpreferably is formed of aluminum or another light weight material suchas a hard plastic or resin. As shown in FIG. 10, an air supply hose 134,which suitably is one and one quarter inches in diameter, carriespressurized air from blower 66 to chamber 132 of main body 130. A firstend wall 136 is defined at one narrow end of main body 130, and a secondend wall (not shown) is defined at the opposite end of main body 130. Aconventional pressure check valve 138 such as shown in FIG. 13 forexample, is provided in each end wall to permit technicians to gauge thepressure inside chamber 132.

One section of main body 130 defines a mounting wall 140 on which aplurality of pressure control valves 162 (such as shown in FIGS. 7 and 8for example and described in detail hereafter) can be mounted. Aplurality of ports 142 are defined through the mounting wall and spacedsufficiently apart from one another to permit side-by-side mounting ofpressure control valves 162. Each port 142 has a bushing 144 mountedtherein. The bushing is configured to receive and secure a valve stem146 (FIG. 8) of a pressure control valve 162. As shown in FIG. 7 forexample, valve stem 146 typically has one or more 0-rings 148 engagewith bushing 144 to form an airtight connection that nonetheless iseasily detachable and engageable, respectively, by manual removal andinsertion of the pressure control valve. This permits easy removal andreplacement of the valve and reduces repair time and inoperative timefor the patient support system as a whole.

The log manifold further includes a circuit board 150 preferably mountedon the exterior of the main body adjacent the mounting wall 140. Asshown in FIG. 10 for example, an electrical connector 152 is providedfor receiving a direct current power line to furnish electric power tooperate circuit board 150. The circuit board includes a plurality ofelectrical connection fittings defined therein. Each electricalconnection fitting 154 or plug outlet is preferably disposed inconvenient registry with one of the ports 142 defined in the mountingwall. Electrical connection fittings 154 receive an electricalconnector, e.g., plug 156, of a pressure control valve 162 to transmitelectrical power and signals thereto to operate the various electricalcomponents of the pressure control valve. In addition, a plurality offuses 158 are provided on circuit board 150 to protect circuit board 150and components connected thereto, such as a microprocessor 160(described hereinafter), from electrical damage. As shown in FIG. 10 forexample, the fuse receptacles are on the exterior of the log manifold128 to provide technicians with the unobstructed access that facilitatestroubleshooting and fuse replacement.

In further accordance with the patient support system of the presentinvention, means are provided for maintaining a predetermined pressurein the sacks. The predetermined pressure is kept at a constantpredetermined value for each of a number of groups of sacks in thestandard mode of operation or may be constantly varying over time in apredetermined sequence in yet other modes of operation of the patientsupport system of the present invention. As embodied herein and shownschematically in FIG. 12 (in which electrical connections are shown indashed lines and pneumatic connections are shown in solid lines, in bothcases arrows indicate the direction of electrical or pneumatic flow) forexample, the means for maintaining a predetermined pressure preferablyincludes a programmable microprocessor processor 160 and at least oneand preferably a plurality of pressure control valves 162, each of thelatter preferably monitored by a pressure sensing device (not shown inFIG. 12 separately from valves 162).

As embodied herein and shown in FIGS. 7 and 8 for example, the means formaintaining a predetermined pressure in the sacks includes a pressurecontrol valve 162. Preferably, a plurality of pressure control valvesare provided, and each valve 162 can control the pressure in a pluralityof sacks 34 by means of being connected to a gas manifold (such asmodular support member channels 100, 102, 104) which carries air fromthe pressure control valve to each of the sacks.

Each pressure control valve includes a housing 164, which preferably isformed of aluminum or another light weight material. As shown in FIG. 8for example, an inlet 166 is defined through one end of the housing forreceiving air flow from a source of pressurized air. An outlet 168 isalso defined through the housing for permitting the escape of airexiting the pressure control valve. An elongated valve passage 170 isdefined within the housing and is preferably disposed in axial alignmentwith the inlet. The passage has a longitudinal axis that preferably isdisposed perpendicularly with respect to the axis of the valve outlet,which is connected to the valve passage. The valve housing furtherdefines a chamber 172 disposed between the inlet and a first end 174 ofthe valve passage. The pressure control valve includes a piston 176disposed in the chamber. The piston is displaceable in the chamber tovary the degree of communication through the chamber that is permittedbetween the valve inlet and the valve passage. The piston preferably isformed of a hard polymeric or resinous material such as polycarbonatefor example. The pressure control valve further includes an electricmotor 178 that preferably is mounted outside the housing and near thechamber.

The pressure control valve preferably includes means for connecting themotor to the piston in a manner such that the operation of the motorcauses displacement of the piston within the chamber. As embodied hereinand shown in FIG. 8 for example, the connecting means preferablyincludes a connecting shaft 180 that has one end non-rotatably securedto the rotatable shaft 182 of the motor 178. Connecting shaft 180 hasits opposite end non-rotatably connected to one end of the piston. Asshown in FIG. 9b for example, piston 176 has a groove 183 disposeddiametrically through one end of the piston to non-rotatably secure theend of connecting shaft 180 therein. Chamber 172 preferably iscylindrical and has its longitudinal axis disposed perpendicularlyrelative to the longitudinal axis of the valve passage. The pistonpreferably is cylindrical and rotatably displaceable in the chamber witha close clearance between the piston and the chamber so as to minimizeany passage of air thereby. One end of the piston has a cam stop 181which engages a stop (not shown) in chamber 172 to restrict piston 176from rotating 360° within chamber 172. As the motor shaft 182 rotates,the connecting shaft 180 and piston 176 are rotatably displaced relativeto the chamber. As shown in FIG. 8 for example, the piston has a flowslot 184 extending radially into the center of the piston so thatdepending upon the position of this slot 184 relative to the inlet andthe passage, more or less flow is allowed to pass from the inlet 166,through this slot 184, and into the passage 170. Thus, the position ofthe piston within the chamber determines the degree of communicationthat is permitted through the chamber and the degree of communicationpermitted between the valve passage and the valve inlet. This degree ofcommunication effectively regulates the pressure of the air delivered bythe valve.

As shown in FIGS. 9a, 9b, 9c, and 9d for example, piston slot 184preferably is configured to result in a linear relationship between theair flow permitted through the valve and the rotation of the piston. Asshown in FIG. 9d for example, piston slot 184 preferably comprises threedistinctly shaped sections. The section designated 185 is closest to thesurface of the piston and is formed as a spheroidal section. Theintermediate section is designated 187 and is formed as a semicylinder.The section extending deepest into the center of the piston isdesignated 189 and is formed as an elongated cylinder with a sphericalend.

As shown in FIGS. 7 and 8 for example, the pressure control valvefurther preferably includes a pressure transducer 186 that communicateswith the valve passage to sense the pressure therein. Preferably, thepressure transducer is mounted to the valve housing. An opening 188 isdefined through the housing opposite where the outlet is defined. Thepressure transducer has a probe (not shown) adjacent the opening topermit the transducer to sense the pressure in the valve passage. Thepressure transducer converts the pressure sensed in the valve passageinto an electrical signal such as an analog voltage, and this voltage istransmitted to an electronic circuit (described hereafter as a circuitcard) of the valve.

As shown in FIG. 7 for example, the pressure control valve furtherincludes an electronic circuit 190 which is mounted to the exterior ofthe housing on a circuit card 192. The valve circuit contains a voltagecomparator network and voltage reference chips for example. The valvecircuit controls the power being provided to the valve motor. Thecircuit card is connected to the valve pressure transducer and receivesthe electrical signals transmitted from the transducer corresponding tothe pressure being sensed by the transducer in the valve passage. Thecircuit card receives a reference voltage signal from a microprocessor(described hereinafter) via circuit board 150. The microprocessor sendsan analog voltage signal to the valve circuit 190 via circuit board 150.The valve circuit compares this signal to the one from the pressuretransducer and computes a difference signal. The valve circuit controlsthe valve motor 178 to open or close the valve according to themagnitude and sign (plus or minus) of the difference voltage signal.

As shown in FIG. 7 for example, The pressure control valve furtherincludes an electrical lead 194 that is connected at one end (not shown)to the valve circuit card 192 and terminates at the other end in a plug156. This plug can be connected into a plug outlet such as theelectrical connection fitting 154 on the log manifold 128 and thus isconsistent with the modular construction of the present invention.

As shown in FIG. 7 for example, the pressure control valve furtherdefines a dump outlet hole 196 through the valve housing in the vicinityof the valve chamber. As shown in FIG. 8 for example, a dump passage 198is defined through the valve piston and is configured to connect thedump hole to the valve passage upon displacement of the piston such thatthe dump hole becomes aligned with the dump passage of the piston.

As shown in FIG. 1 for example, a microswitch 199 is disposed near thehydraulic controls for changing the elevation of the patient support.When a control handle 201 is placed in the CPR mode of operation,microswitch 199 is activated, and the microprocessor turns off theblower and signals all of the valves to align the dump passage of thepiston with the dump hole. This causes the rapid deflation of all of theair sacks and places the support into a condition suitable forperforming a cardiopulmonary resuscitation (CPR) procedure on thepatient.

As shown in FIG. 16 for example, the control panel of the presentinvention has a button for SEAT DEFLATE. When the operator presses theSEAT DEFLATE button, the microprocessor activates the two pressurecontrol valves which control the pressure in the sacks supporting theseat zone (Zone III shown in FIGS. 12 and 13 for example) of the supportsystem. The microprocessor signals the pressure control valvescontrolling the seat zone to align their pistons' dump passages with thedump holes in the valve housings in order to permit all of the air inthe sacks in the seat zone to escape to the atmosphere through the dumpholes. As shown in FIG. 8 for example, when the valve pistons arealigned in this manner, the valve inlets are blocked by the pistons andthus prevented from communicating with the valve passages and valveoutlets.

As shown in FIG. 8 for example, a conventional pressure check valve 138preferably is mounted in a manual pressure check opening 200 definedthrough the housing of each pressure control valve. As shown in FIG. 9,a conventional pressure check valve 138 also preferably is inserted intothe end walls of log manifold 128. As shown in FIG. 15 for example,check valve 138 has a head 202 with a port 204 defined therethrough forreceiving a probe of a pressure measuring instrument (not shown). Acollapsible bladder flange 206 extends from head 202 to the opposite endof check valve 138. The bladder flange extends through the pressurecheck opening 200 in the housing of the pressure control valve. A slit208 is formed axially through the collapsible bladder flange andconnects to port 204. The bladder flange is resiliently collapsiblearound slit 208 to prevent passage of air therethrough. The probe of themeasuring instrument is hollow and is inserted through port 204 untilthe probe parts the flange 206 to open the collapsible slit 208. Thisallows the probe to access the pressure in the control valve or chamberof the log manifold, as the case may be. Check valve 138 preferably isformed of a flexible material such as a soft plastic or neoprene rubber.One supplier of such check valves is Vernay Labs of Yellow Springs, Ohio45387.

As embodied herein and shown schematically in FIG. 12 for example, themeans for maintaining a predetermined pressure preferably includes aprogrammable microprocessor 160. The microprocessor preferably hasparallel processing capability and is programmed to operate the pressurecontrol valves in conjunction with the blower to pressurize the sacksaccording to the height and weight of the patient. The height and weightinformation is provided to the microprocessor by the operator. This isaccomplished by providing the desired information via a control panel210 such as shown in FIG. 16 for example. The height of the patient isdisplayed on a digital readout 212 in either inches or centimeters, andthe weight of the patient is displayed on a separate digital readout 214in either pounds or kilograms.

As shown in FIGS. 12 and 13 for example, five pressure zones or bodyzones preferably include a head zone (Zone 1 or I), a chest zone (Zone 2or II), a seat zone (Zone 3 or III), a thigh zone (Zone 4 or IV), and aleg and foot zone (Zone 5 or V). Each body zone is supplied withpressurized air from the blower via two separate pressure controlvalves. In one configuration of the air flow path from the blower to thesacks, one of the pressure control valves controls air supplied to thechambers of each sack on one side of the patient support system for eachbody zone, and the other pressure control valve controls the air to thechambers on the side of each sack on the opposite side of the patientsupport system. In yet another configuration of the air flow path fromthe blower to the sacks, one of the pressure control valves controls theair supplied to all of the chambers of every alternate sack in a bodyzone, and the other pressure control valve controls the air supplied toall of the chambers in the remaining alternate sacks in the body zone.

The microprocessor is programmed to set the reference pressure of eachpressure control valve of each body zone into which the patient supportsystem has been divided for purposes of controlling the pressuresupplied to air sacks 34 under particular portions of the patient. Basedupon the height and weight of the patient, the microprocessor ispreprogrammed to calculate an optimum reference pressure for supportingthe patient in each body zone. This reference pressure is determined atthe valve passage where the pressure transducer of each pressure controlvalve is sensing the pressure. The circuit card 192 performs acomparison function in which it compares the reference pressure signaltransmitted to it from microprocessor 160 via circuit board 150 to thepressure which it has received from the pressure transducer. Dependingupon the difference between this signal received from the valve'spressure transducer and the calculated desired signal corresponding tothe preset reference pressure, the valve circuit 192 signals the valvemotor to open or close the pressure control valve, depending uponwhether the pressure is to be increased or decreased. This processcontinues until the desired reference pressure is sensed by the pressuretransducer of the pressure control valve. The microprocessor hasparallel processing capability and thus can simultaneously supply eachof the pressure control valves with the reference pressure for thatparticular control valve. Moreover, the speed of each of themicroprocessor and valve circuits greatly exceeds the time in which themotors of the pressure control valves can respond to the signalsreceived from the valve circuits. Thus, in practical effect the motorresponse times limit the frequency with which the pressure controlvalves can be corrected.

Moreover, the reference pressure calculated by the microprocessor alsocan depend upon other factors such as whether one or more articulatablesections of the frame is elevated at an angle above or below thehorizontal. Another factor which can affect the microprocessor'scalculation of the reference pressure for the particular zone is whetherthe patient is being supported in a tilted attitude at an angle belowthe horizontal and whether this angle is tilted to the left side of thepatient support system or the right side. Still another factor iswhether the patient is lying on his/her side or back.

Yet another factor that can affect the reference pressure calculated bythe microprocessor is whether the patient comfort adjustment buttons 216have been manipulated via the control panel to adjust the pressuredesired by the patient in a particular zone to a pressure slightly aboveor slightly below the reference pressure that the microprocessor ispreprogrammed to set for that particular zone under the other conditionsnoted, including, elevation angle, side lying or back lying, and tiltattitude. As shown in FIG. 16 for example, each body support zone has atriangular button 216 pointing upward and a triangular button 216pointing downward. Depression of the upward button 216 increases thereference pressure that the microprocessor calculates for thatparticular zone. Similarly, the depression of the downward pointingbutton 216, decreases the reference pressure that the microprocessorcalculates for that particular zone. The range of increase and decreasepreferably is about twenty percent of the reference pressure that iscalculated for the standard mode of operation in each particular zone.This permits the patient to change the pressure noticeably, yet not somuch as to endanger the patient by producing a condition that is eitherover-inflated or under-inflated for the sacks in a particular zone.Moreover, the 20% limitation also can be overridden by pressing theOVERRIDE button shown in FIG. 16. The override function can be cancelledby pressing the RESET button shown in FIG. 16.

One form of sack pressure algorithm which is suitable for use by themicroprocessor to calculate the reference pressures for differentconfigurations of the patient support system of the present invention isas follows:

    Pressure=C.sub.1 ×Weight+C.sub.2 ×Height+C.sub.3

Table 1 provides parameters suitable for several elevationconfigurations, patients lying on his/her back, side lying, and all fivezones. For example, the constants C1, C2 and C3 for each zone are thesame for elevation angles 0° through 29° with the patient lying onhis/her back. The values of C1, C2 and C3 for side lying are the samefor elevation angles of 0° through 29° .

                  TABLE 1                                                         ______________________________________                                        Elevation                                                                     Angle       Zone   C1        C2     C3                                        ______________________________________                                        0°-29°                                                                      I      0.00473   0.04208                                                                              -1.27789                                  back lying  II     0.02088   -0.01288                                                                             1.73891                                               III    0.03688   -0.10931                                                                             7.33525                                               IV     0.00778   -0.01828                                                                             2.21268                                               V      0.00316   0.00482                                                                              0.61751                                   30°-44°                                                                     I      0.00857   0.02056                                                                              -0.22725                                  back lying  II     0.02230   -0.03996                                                                             3.32860                                               III    0.01971   0.08197                                                                              -0.68941                                              IV     0.00554   0.03495                                                                              0.38316                                               V      0.00303   0.01883                                                                              -0.12248                                  45°-59°                                                                     I      0.00152   0.02889                                                                              0.11170                                   back lying  II     0.01349   -0.02296                                                                             3.06615                                               III    0.03714   0.01023                                                                              3.37064                                               IV     0.01014   0.09399                                                                              -3.39696                                              V      0.00298   -0.00337                                                                             1.40102                                   60° and above                                                                      I      0.00571   -0.00976                                                                             1.77230                                   back lying  II     0.01165   0.02598                                                                              -0.20917                                              III    0.01871   0.04853                                                                              4.35063                                               IV     0.02273   0.06610                                                                              -2.94674                                              V      0.00291   0.00292                                                                              0.99296                                   SL          I      0.01175   0.00548                                                                              0.43111                                   (Side       II     0.03276   0.03607                                                                              -1.78899                                  Lying)      III    0.03715   -0.10824                                                                             8.22602                                   0°-29°                                                                      IV     0.01091   -0.00336                                                                             1.48258                                               V      0.00146   0.02093                                                                              -0.15271                                  ______________________________________                                    

The weight of the patient is supported by the surface tension of the airsack as well as the air pressure within the sack. Thus, values of C1,C2, and C3 can vary with air sack geometry or the properties, such asstiffness, of the materials used to form the air sack. Different airsack geometries may provide more or less stiffness in the air sack.

Typically, a ribbon cable 218 electrical connector (FIG. 10) connectscircuit board 150 to microprocessor 160. Circuit board 150 receivesanalog signals from microprocessor 160 and distributes same to the valvecircuit card 192 of each particular pressure control valve 162 for whichthe signal is intended. In addition, in some embodiments, circuit board150 can return signals from the individual pressure control valvecircuitry 190 to the microprocessor. The voltage signals from themicroprocessor cause the valve circuit card 192 to operate the motor ofthe pressure control valve to expand or contract the valve opening toattain a reference pressure, which the microprocessor is preprogrammedto calculate. The valve circuit compares the reference signal receivedfrom the microprocessor to the signals received from pressure transducer186 of the pressure control valve. In effect, this enables the supportsystem of the present invention to monitor the air pressure in the valvepassage 170 near the valve outlet 168, which is the location where thesensing probe of the pressure transducer is disposed to sense thepressure supplied to the air sack through the pressure control valve.

In further accordance with the present invention, there is providedmeans for switching between different modes of pressurizing the sacks.As embodied herein and shown schematically in FIGS. 11, 12 and 13 forexample, the mode switching means preferably includes at least one flowdiverter valve 220 and preferably includes a plurality of flow divertervalves 220. The number of flow diverter valves depends upon the numberof different pressure zones desired for the patient support systemembodiment contemplated. A pressure zone includes one or more sacks orsack chambers which are to be maintained with the same pressurecharacteristics. In some instances, it is desired to have opposite sidesof the sack maintained at different pressures. This becomes desireablefor example when the rotation mode of the patient support system isoperated. In other instances it becomes desireable to have the pressurein every other sack alternately increasing together for a predeterminedtime interval and decreasing together for a predetermined time interval.This becomes desireable for example when the patient support system isoperated in the pulsation mode of operation.

As shown in FIG. 13 for example, each flow diverter valve preferably ismounted within a modular support member 68, and more than one divertervalve 220 can be mounted in a modular support member such as the seatsack support member 94. However, other sack support members 68, such asthe head sack support member shown in FIG. 13 for example, may lack adiverter valve. Each diverter valve preferably is mounted between thetop and bottom surfaces of each plate 70. As shown schematically in FIG.11 for example, each diverter valve has a first flow pathway 222 with afirst inlet 224 at one end and a first outlet 226 at the opposite end.Each diverter valve further includes a second flow pathway 228 with asecond inlet 230 at one end and a second outlet 232 at the opposite end.The flow pathways are mounted and fixed on a rotating disk 234, alsoreferred to as a switching disk 234, that rotates about a central pivot236.

The so-called switching disk is rotatable for the purpose of changingthe path defined by the inlets and outlets. As shown in solid lines inFIG. 11 for example, first flow pathway 222 connects channel A withchannel B, and second flow pathway connects channel C with channel D.Thus, a first inlet 224 of first pathway 222 is connected to channel Aand a first outlet 226 of first pathway 222 is connected to channel B.Similarly, a first inlet 230 of second pathway 228 is connected tochannel D and a first outlet 232 of second pathway 228 is connected tochannel C. In the solid line configuration shown schematically in FIG.11, both sides of every alternate sack are connected together and thusmaintained at the same pressure by a pressure control valve connected tothe sacks via pressure control valve openings 96 This is theconfiguration for the so-called pulsation (P) mode of operation.

As shown by the dotted line configuration of the flow pathways, when theswitching disk is rotated 90° counterclockwise to the dotted lineposition (R), the first flow pathway connects channel A to channel C,and the second flow pathway connects channel B to channel D. Thus, firstinlet 224 of first pathway 222 is connected to channel C, and secondinlet 230 of second pathway 228 is connected to channel B. First outlet226 of first pathway 222 becomes connected to channel A, and secondoutlet 232 of second pathway 228 becomes connected to channel D. In thedotted line configuration shown in FIG. 11, one side of all of the sacksare connected together and thus can be maintained at a common pressure,and the other side of all of the sacks are connected together and alsocan be maintained at a common pressure. This is the configuration forthe so-called rotation (R) mode of operation.

The use of the diverter valves by the present invention enables thesupport system to be operated in either a pulsation mode of operation ora rotation mode of operation with a minimum number of valves and airflow conduits. The diverter valve allows the air flow paths of thesupport system to be reconfigured between two distinctly different waysof connecting the pressurized air source through the pressure controlvalves to individual air sacks of the patient support system.

The patient support system of the present invention can be operated toautomatically rotate the patient, i.e., turn the patient to one side orthe other, at preset intervals of time. Referring to the control panelshown in FIG. 16, the patient support system of the present inventioncan be set to operate in a rotational mode by pressing the SET UP buttonfollowed by pressing the MODE SELECTION button until the ROTATIONindicator is lit. Then the rotation section of the control panel becomesilluminated and can be operated. The operator selects the amount of timethat the patient is to be maintained in a right-tilted position, or ahorizontal position, or a left-tilted position. To accomplish this forthe horizontal position for example, the operator activates thehorizontal button 238 followed by activating the TIME button. Thismanipulation enters the time interval during which the patient supportis to maintain the patient supported in the horizontal position. Thisinterval of time is displayed on a digital readout 239. To set the timethat the patient is to spend in the right-tilted position, the operatorpresses the right button 240 followed by the TIME button. Again, thetime interval which the patient is to be maintained tilted to the rightis displayed digitally on readout 239. A similar procedure is followedto set the time spent in the left-tilted position.

In addition, right button 240 allows the operator to select the attitudeof the patient in the right-tilted position. There are a number ofillumination bars disposed above the right button. Each illumination barcorresponds to a different attitude to which the patient can be tiltedto the right. The operator selects the desired attitude by continuouslypressing the triangular buttons above and below right button 240 untilthe bar adjacent the desired attitude is illuminated. For example, themaximum attitude of tilt requires the operator to continue pressing thedownward pointing triangular button beneath right button 240 until thelowermost bar above the right button is lit. The same procedure isfollowed to set the attitude for the left-tilted position.

Moreover, as shown schematically in FIG. 12 for example, the angle ofelevation of the head and chest section of the patient support ismonitored by an elevation sensing device 242, which sends signals to thecircuit board 150 of the modular valve mounting manifold 128. FIG. 12illustrates electrical signaling pathways by dashed lines and pneumaticpathways by solid lines. The arrows at the ends of the dotted linesindicate the direction of the electrical signals along the electricalpathways. The elevation sensing device detects the angle at which thehead and chest section has been positioned, and supplies a correspondingsignal to the microprocessor via circuit board 150. Examples of suitableelevation sensing devices are disclosed in U.S. Pat. Nos. 4,745,647 and4,768,249, which patents are hereby incorporated in their entiretiesherein by reference. If this elevation information from the sensingdevice 242 indicates that the angle of articulation exceeds 30° themicroprocessor configures the pressure profile to a standard mode ofoperation and thus cancels any rotation or pulsation that may have beenselected by the operator. The rotation mode is cancelled to avoidtorquing the patient's body. The pulsation mode is cancelled because theelevation of the patient above 30° reduces the ability to float thepatient in the sacks in the seat zone during pulsation of the threesacks therein. Thus, the "bottoming" of the patient during pulsation atelevation angles above 30° is avoided. Upon reduction of the articulatedangle below 30° , the microprocessor does not automatically resumeeither pulsation or rotation but requires any mode other than thestandard mode to be reset.

In accordance with the present invention, the control over blower 66preferably includes a blower control circuit which controls the powersupplied to blower 66. Microprocessor 160 provides a blower controlvoltage to blower control circuit 67 which controls the power supply toblower 66 according to this blower control voltage signal received frommicroprocessor 160. A pressure transducer 246 measures the pressurepreferably at the blower and communicates a signal corresponding to themeasured blower pressure to the microprocessor 160 via blower controlcircuit 67 and circuit board 150.

Microprocessor 160 has a blower control algorithm which enablesmicroprocessor 160 to calculate a desired reference pressure for theblower. The blower control algorithm preferably calculates this blowerreference pressure to be 3 to 4 inches of standard water higher than thehighest pressure in the air sacks. Typically, the seat zone (Zone III)has this highest pressure for a given height and weight setting(provided by the operator to the microprocessor) regardless of theelevation of the head and chest sections and whether the patient islying on his/her side or back. However, a patient with abnormal bodymass distribution (which could be caused by a cast for example) mayrequire the highest sack pressure in one of the other zones. If Zone IIIhas the highest sack pressure, as the elevation angle increases, thesack pressure in Zone III increases, and the reference pressure for theblower also increases to equal 3 to 4 inches of standard water above thepressure of the sacks in Zone III.

Microprocessor 160 stores the signal from transducer 246 correspondingto the measured blower pressure in the microprocessor memory, which isupdated preferably only once every three seconds. Microprocessor 160calculates the reference blower pressure about four times each secondand compares it to the stored measured pressure about once each second.If the measured pressure is more than about one inch of standard waterhigher than the reference pressure calculated by microprocessor 160,microprocessor 160 decreases the control voltage by an increment of1/256 of the maximum control voltage signal that microprocessor 160 isprogrammed to provide to blower control circuit 67. This maximum voltagecorresponds to the maximum output of blower 66. If the measured blowerpressure is more than about one inch of standard water lower than thereference pressure, then microprocessor 160 increases the controlvoltage signal by an increment of 4/256 times the maximum controlvoltage. The increase or decrease, if any, occurs about once eachsecond. Pressure deficits are of a greater concern, and thus correctionof such deficits occurs four times faster than correction of excesspressures. The pressure changes resulting from the blower controlsequence occur no more frequently than once each second and are nogreater than 1/256 of the maximum pressure for decreases and 4/256 timesthe maximum pressure for increases. Moreover, the microprocessor's threesecond delay in updating the measured pressure used in the calculationsassures that changes in the measured pressure that have very shortdurations will not lead to pressure instability because of control loopexacerbation of short-lived pressure fluctuations. This three secondtime interval can change depending upon the pressure dynamics andcontrol dynamics of the system.

The selection of the rotation mode of operation on control panel 210causes the microprocessor to signal the diverter valves to align theirpathways for rotational operation of the support system. Once theparameters of operation in the rotation mode have been inputted, themicroprocessor recalculates an optimum reference pressure for eachpressure control valve. The microprocessor determines the appropriatetilt reference pressure based upon the height and weight of the patientand the angle of tilt selected by the operator. This is accomplishedsuch that the pressure in the low pressure side of the sack and thepressure in the high pressure side of the sack average out to thepressure that would be set for the same sacks in the normal mode ofoperation, i.e., without any rotation. Thus, the average pressure overthe entire sack during the rotational mode of operation is the same asit would be in the non-rotational modes of operation.

The operator initiates the rotation by pressing the RUN button on panel210 in FIG. 16 for example. When the operator presses the RUN button,the microprocessor adjusts the pressure control valves 162 to set thenew tilt reference pressure in the end and intermediate chambers on theside of the support system to be tilted. This results in a reduction inthe pressure in the end and intermediate chambers of the tilted sides ofthe sacks in each body zone. The microprocessor operates the controlvalve to prevent this low sack pressure from falling below 1 to 2 inchesof standard water, because this is the minimum pressure needed to keepthe end chamber inflated while the weight of the patient is squeezingout air from the intermediate chamber. The microprocessor also raisesthe pressure in the end and intermediate chambers on the opposite side,i.e., non-tilted side of the sacks of the support system. The increasein pressure in the chambers of the untilted side of the support systemis needed to compensate for the loss in pressure in the chambers on thetilted side of the support system. The additional pressure allows thepatient to be supported in the tilted position as comfortably as in thenon-tilted position. The pressure increase in the chambers of thenon-tilted side of the sacks is preferably sufficient so that theaverage pressure between the two sides of each sack equals the pressurein this sack when the patient is supported thereon in a non-tiltedposition. In other words, one-half of the sum of the pressure in thehigh side of the sack and the low side of the sack is equal to thenormal base line pressure of this particular sack in a non-tilted modeof operation, i.e., when both sides of the sack are at this same baseline pressure.

In accordance with the present invention, a method is provided forturning the patient on a low air loss patient support system as in thepresent invention. As embodied herein, the turning method includes thestep of grouping all of the sacks 34 into at least two body zones thatcorrespond to at least two different zones of the patient's body. Eachzone of the patient's body is preferably supported by one or more sacksin one of the two body zones. Preferably five body zones are involved.

The next step in the method for turning a patient is to pressurize allof the sacks according to a first pressure profile that provides eachsack in each body zone with a respective first air pressure. This firstair pressure has been chosen so as to provide a first respective levelof support to that portion of the patient's body supported by the sacksin that body zone. The level of support is predetermined depending uponthe height and weight of the patient and calculated accordingly by themicroprocessor. The height and weight data also affect the respectivefirst air pressure that is chosen for the sacks in that particular bodyzone.

The terms "pressure profile" are used to refer to the fact that thepressure in each body zone may be different because of the differentsupport requirement of that particular body zone. If the individualpressures in the sacks of all the body zones were to be represented on abar graph as a function of the linear position of the sacks along thelength of the patient support, a line connecting the tops of the bars inthe graph would depict a certain profile. Hence the use of the term"pressure profile" to describe the pressure conditions in all of thesacks at a given moment in time, either when the pressures are changingor in a steady state condition.

The next step in turning the patient involves separately controlling theair pressure that is supplied to each side of each of the sacks. Thispreferably is accomplished by supplying the chambers on one side of thesacks in each body zone via a first pressure control valve and supplyingthe chambers on the other side of the sacks via a separate pressurecontrol valve, and connecting each pressure control valve to a four-waydiverter valve. The diverter valve can then be configured to ensure thatthe air pressure being supplied to the chambers on one side of each sackis being controlled by one of the pressure control valves, and thepressure being supplied to the chambers on the other side of the sack ofa particular zone is being supplied through a separate pressure controlvalve.

The next step in turning the patient involves lowering the pressure inthe chambers on the side of the sacks to which the patient is to betilted. Specifically, the pressure must be lowered in the chambers ofone side of the sacks from a first pressure profile, previouslyestablished, to a predetermined second pressure profile. The secondpressure profile is predetermined according to the height and weight ofthe patient and also according to the attitude to which the patient isto be tilted. The greater the angle below the horizontal to which thepatient is to be tilted, the lower the predetermined second pressureprofile.

Another step in the method of turning the patient requires raising thepressure in the chamber on the side of the sacks that is opposite theside to which the patient is being tilted. This involves raising thepressure in the chamber of the non-tilted side of each of the sacks to apredetermined third pressure profile. The raised pressure profile in thenon-tilted sacks compensates for the lower pressure profile in the sideof the sacks to which the patient has been tilted. When the overallpressure being supplied to support the patient has been reduced in halfof the sack, as occurs during tilting, that portion of the patient'sbody in that particular body zone would not be maintained at the desiredlevel of support without increasing the pressure in the non-tilted sideof the sack.

The operator begins by lowering the pressure in one side of the all ofthe sacks until the patient has been tilted to the desired attitude oftilt beneath the horizontal. As this is occurring, the microprocessor isincreasing the pressure in the non-tilted sacks such that one-half ofthe sum of the pressure in the tilted sacks plus the pressure in theuntilted sacks equals the base line pressure of the sacks before thetilting procedure began. In the case just described, the base linepressure corresponds to the pressure in the sack at the first pressureprofile. Preferably, the raising and lowering of the pressures in thechambers of opposite sides of the sacks occurs practicallysimultaneously. Since preferably the microprocessor has parallelprocessing capability and thus can control each of the pressure controlvalves simultaneously, the speed with which the tilting is effected (orany other pressure changes in the sacks) is primarily limited by theflow restrictions in the pneumatic circuit, which is primarily afunction of the air sack volume and the pressure level in the sacks.

In further accordance with the present invention, the patient ismaintained in the selected tilted position for a predetermined length oftime. At the end of this predetermined length of time, which is clockedby the microprocessor, the patient is returned to the horizontalposition by simultaneously increasing the pressure in the side of thesacks to which the patient previously had been tilted while decreasingthe pressure in the non-tilted side of the sacks until the pressure inboth sides of the sacks returns to the first predetermined pressureprofile. The changes in pressure from low to high or from high to lowpreferably occurs over a time interval of about three minutes. This isdone to reduce the likelihood that the patient will experience anyuncomfortable sensation during these pressure changes.

In still further accordance with the present invention, the method ofturning a patient can maintain the patient in the horizontal positionfor a predetermined interval of time. At the end of this predeterminedinterval of time, the patient then can be tilted to the side of thepatient support system that is opposite the side to which the patienthad been tilted prior to being maintained in the horizontal position.Moreover, the amount of time which the patient spends in a particularposition, namely, left-tilted, horizontal, and right-tilted, can bepreselected so that the patient can be maintained in one of the threepositions for however long is deemed therapeutic.

It is during the turning, i.e., rotation or tilting, mode of operationthat the grommet which defines the hole 64 connecting each intermediatechamber 54 with each end chamber 46 of each sack 34 plays a particularlyimportant role. As the pressure control valve controlling the side ofthe sack to which the patient is to be tilted begins to close and reducethe pressure being supplied to this side of these sacks, the weight ofthe patient above the depressurizing intermediate chamber 54 squeezesthe air from the intermediate chamber through the grommet and into theend chamber 46 to compensate for the reduced pressure being supplied tothe end chamber via the pressure control valve. Thus, the reduction inpressure initially serves to deflate the intermediate chamber whilemaintaining the end chamber as fully inflated as before the pressurecontrol valve began to reduce the pressure supplied thereto. Thepressure in the end chamber of course is being reduced. However, the endchamber remains completely inflated, unlike the connecting intermediatechamber which is being squeezed by the weight of the patient that nolonger is being supported by the same level of air pressure as waspresent when the sacks were being maintained according to the firstpressure profile that was first set to maintain the patient in thehorizontal position atop the sacks. Moreover, since the end chamberremains inflated, it acts as a passive constraint to prevent the patientfrom rolling past the end chamber and off of the patient support.

To operate the support system of the present invention in the pulsationmode, the operator pushes the SET UP button on the control panelillustrated in FIG. 16 for example. Then the operator presses the MODESELECTION button until the PULSATION indicator illuminates. When thePULSATION indicator is illuminated, the pulsation section of the controlpanel also becomes illuminated. The microprocessor immediately signalsthe diverter valves to align their pathways for the pulsation mode ofoperation. In the pulsation alignment of the diverter valves, thechannels of the modular support members connect alternately adjacent airsacks. This results in two sets of sacks which can be operated at twoseparate and opposite patterns of pressurization. As shown in FIG. 16for example, the operator selects the time interval for a completepulsation cycle by pressing the TIME button. The time interval for eachpulsation cycle is displayed in a digital readout 244 above the TIMEbutton. The operator selects the degree of depressurization in the phaseof the pulsation cycle in which the pressures in alternating sacks arelowered while the pressures in the other sacks are increased accordingto the amount that the pressures in the first group of alternating sackshave been lowered. The operator accomplishes this selection by pressingone of the two triangular shaped buttons beneath the light bars next tothe MAX-MIN scale to illuminate the light bar adjacent the desired levelof depressurization. Once the parameters of operation in the pulsationmode have been inputted, the microprocessor begins calculating apulsation reference pressure for each pressure control valve. Thispulsation reference pressure depends upon the degree of depressurizationselected by the operator and the height and weight of the patient.Preferably, the microprocessor maintains the pressures in adjacent sackssuch that one-half of the sum of the pressures in the adjacent sacksequals the base line pressure for a sack in that zone at the elevationangle, if any, and taking into account whether the patient is side lyingor back lying. The operator initiates the pulsation of the sacks bypressing the RUN button on panel 210 in FIG. 16 for example.

In further accordance with the present invention, a method is providedfor periodically relieving the pressure of the patient support systemagainst the patient's body. This method preferably is accomplished bypulsating the pressure in the sacks of the low air loss patient supportsystem having a plurality of sacks disposed transversely across thelength of the support system. The pressure in a first group of sackscomprising every alternating sack is depressurized relative to theremaining sacks, which are provided with an increase in pressure. Thepressure differential between the two separate sacks is maintained for apredetermined interval of time. At the end of this time interval, thepressure profiles switch so that the other set of alternating sacksbecomes depressurized while the first set of alternating sacks receivesa slight increase in pressure. This opposite pressurization condition isalso maintained for a predetermined interval of time, whereupon thecycle repeats itself until the pulsation mode of operation isdiscontinued.

Prior to the initiation of the pulsation mode of operation, all of thesacks in the patient support will be maintained at a first pressureprofile according to the height and weight of the patient, the variousangles of inclination of any of the articulating sections of the frame,and any tilt angle imposed upon the sacks. However, preferably, thepulsation method will not be operated in conjunction with any tilting ofthe patient, and thus activation of the pulsation method automaticallydiscontinues operation in the tilting mode.

The steps of the method for pulsating the pressure in the sacks of thelow air loss patient support system include configuring the air supplymeans of the patient support to define two separate groups ofalternating sacks. A first group of sacks includes either every oddnumber sequenced sack in order from one end of the patient support tothe opposite end of the patient support or every even number sequencedsack. For purposes of this description, the first of the two groups ofsacks will be chosen to be the odd number sequenced sacks. In apreferred embodiment, the sacks are further grouped into body zones tosupport the patient's body at a predetermined pressure for all of thesacks in the body zone. Thus, all of the sacks in a particular body zonewill be pressurized at the same first pressure, and accordingly theindividual first pressure will be applied to all of the sacks in eachbody zone. This step of configuring the sacks is preferably accomplishedby configuring a plurality of diverter valves to connect everyalternating sack in a body zone.

The next step includes reducing the air pressure being supplied to thesacks in the first group. This is accomplished as the microprocessorcontrols the pressure control valve of this first group to attain asecond pressure profile. The second pressure profile corresponds to adecreased pulsation reference pressure calculated by the microprocessorwhen the degree of depressurization was selected by the operator. Themicroprocessor controls the pressure control valves supplying air to thesacks in the first group until the decreased pulsation referencepressure has been attained by the sacks in this first group.

The next step occurs simultaneously with the first step and includessupplying air pressure to the sacks in the second of the two groups,namely, the group including every even number sequenced sack in orderfrom one end of the patient support to the opposite end of the patientsupport, at a third pressure profile. This third pressure profilecorresponds to an increased pulsation reference pressure which themicroprocessor calculated for each pressure control valve controllingthe sacks in the second group for each individual body zone. Thisincreased pulsation reference pressure also has been calculated by themicroprocessor depending upon the degree of depressurization selected bythe operator. This third pressure profile is designed to compensate forthe loss of pressurization by the first group of sacks so that thepatient support can continue to maintain the patient at the same levelof horizontal support during the depressurization of the first group ofsacks. In other words, while the pressures in the alternate groups ofsacks are changing, the vertical height of the patient above the flooris not changing significantly from what it was prior to the onset of thepulsation mode of operation. Thus, the microprocessor maintains thepressures in the two groups of sacks such that one-half the sum of thesecond and third pressure profiles equals the first pressure profile.

The two steps involving the changes in pressurization of the two groupsof sacks, occur simultaneously over a first time interval.

The method for pulsating the pressure in the sacks further includes thestep of maintaining the second and third pressure profiles beingsupplied to the two groups of sacks during a second interval of time.This is accomplished by the microprocessor controlling the pressurecontrol valves to maintain the increased or decreased pulsationreference pressures calculated by the microprocessor for the respectivegroup of sacks over the time interval selected by the operator.

After the predetermined lower pressure has been maintained for the sacksin the one group for the second interval of time, the next step is toincrease the pressure being supplied to this one group during a thirdinterval of time until each sack in this one group attains a higherindividual pressure corresponding to the third pressure profile. At thesame time that the sacks in the first group of sacks are attaining thehigher individual pressure, the pressure being supplied to the sacks inthe other of the two groups is being decreased to the lower pressurecorresponding to the second pressure profile. The pressure in the otherof the two groups is decreased until the predetermined lower pressure isbeing provided to each individual sack in this other group. The pressuredecreases over this third interval of time.

Finally, the third pressure profile in the one group and the secondpressure profile in the other group are maintained during a fourthinterval of time.

Preferably, all of the first, second, third, and fourth intervals oftime are of equal duration. However, in some embodiments of the methodof pulsating the sacks of the present invention, the first interval oftime preferably equals the third interval of time, and the secondinterval of time preferably equals the fourth interval of time.

In yet another embodiment of the method of pulsating the sacks of thepresent invention, not only are the first and third time intervals equalto each other as well as the second and fourth time intervals beingequal to each other, but the first and third time intervals are shorterthan the second and fourth time intervals. In other words, the timewhich the sacks spend alternately changing pressures is less than thetime during which the sacks remain at the steady state higher or lowerpressures. Similarly, in yet another embodiment of the method ofpulsating the sacks of the present invention, the second and fourth timeintervals can be equal to each other and shorter than the first andthird time intervals, which also are equal to each other.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the scope or spirit of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. An apparatus for supporting a patient, theapparatus comprising:(a) a rigid support member; (b) a plurality ofelongated inflatable sacks, each said sack being disposed to extendtransversely across said support member; (c) at least one of saidelongated inflatable sacks having:(i) a pair of end chambers, each endchamber disposed at an opposite end of said sack and being separatelypressurizable, (ii) a pair of intermediate chambers disposed betweensaid end chambers, each said intermediate chamber having a rightpentahedron shape with the diagonal surface facing toward the center ofsaid elongated inflatable sack, and (iii) a first restrictive flowpassage connecting one of said end chambers to said adjacentintermediate chamber, and a second restrictive flow passage connectingsaid second of said pair of end chambers to said second of said pair ofintermediate chambers.
 2. An apparatus as in claim 1, furthercomprising:means for supplying gas to each said sack.
 3. An apparatus asin claim 2, wherein:said means for supplying gas to each said sackincludes:(a) a blower; (b) a blower control circuit connected to saidblower for regulating the power supplied to said blower; (c) amicroprocessor being connected for communicating a first control signalto said blower control circuit, and said blower control circuit beingconfigured to control the power supplied to said blower according tosaid first control signal; (d) a pressure transducer connected tomeasure the pressure of gas exiting said blower and for transmitting asignal corresponding to said measured pressure; (e) said microprocessorbeing programmed for calculating a reference signal corresponding to areference blower pressure and being connected for receiving and storingsaid measured blower pressure signal for a predetermined time interval;(f) said microprocessor being programmed for comparing said calculatedsignal to said measured signal and determining a second control signalaccording to the result of said comparison; and (g) said microprocessorbeing programmed for transmitting said second control signal to saidblower control circuit.
 4. An apparatus as in claim 2, wherein:saidmeans for supplying gas to each said sack includes said rigid supportmember wherein said rigid support member defines a plate having a flattop surface opposite a bottom surface, two opposed ends and two opposedside edges connected between said ends, at least two inlet openingsdefined through one of said side edges, at least two outlet openingsdefined through the other of said side edges, and at least two separatedenclosed channels, each said channel connecting one of said outletopenings with one of said inlet openings, at least two air sack supplyopenings defined through said top surface, each said air sack supplyopening communicating with one of said channels.
 5. An apparatus as inclaim 4, further comprising:means for switching between different modesof pressurizing each said sack.
 6. An apparatus as in claim 5, whereinsaid means for switching between different modes of pressurizing eachsaid sack includes a flow diverter valve having:(a) a first inlet and asecond inlet, (b) a first outlet and a second outlet, (c) a firstpathway connecting said first inlet to said first outlet, (d) a secondpathway connecting said second inlet to said second outlet, and (e)means for switching said pathways such that said first pathway connectssaid first inlet to said second outlet and said second pathway connectssaid second inlet to said first outlet.
 7. An apparatus as in claim 4,wherein:said means for supplying gas to each said sack further includesat least one elongated connection fitting, each said connection fittinghaving an exterior configured to engage air-tightly with said air sacksupply opening and having an interior configured with an axiallyextending coupling opening configured to receive a coupling in air tightengagement therewith.
 8. An apparatus as in claim 1, furthercomprising:means for maintaining a predetermined pressure in each endchamber of each said elongated inflatable sack having same.
 9. Anapparatus as in claim 8, wherein:said means for maintaining apredetermined pressure in each said sack comprises at least one pressurecontrol valve, a pressure sensing device disposed to sense the pressureprovided to each said sack, and a microprocessor connected to saidpressure sensing device to receive signals therefrom, saidmicroprocessor being connected to control said pressure control valve.10. An apparatus as in claim 1, further comprising:(a) a source ofpressurized air; (b) a flow diverter valve having:(i) a first inlet anda second inlet, (ii) a first outlet and a second outlet, (iii) a firstpath connecting said first inlet to said first outlet, (iv) a secondpath connecting said second inlet to said second outlet, and (v) meansfor switching said paths such that said first path connects said firstinlet to said second outlet and said second path connects said secondinlet to said first outlet; (c) a first pressure control valve having afirst output end communicating with one of said inlets and having afirst input end communicating with said source of pressurized air; and(d) a second pressure control valve having a second output endcommunicating with the other of said inlets and having a second inputend communicating with said source of pressurized air.
 11. An apparatusfor supporting a patient, the apparatus comprising:(a) a frame having atleast one articulatable section; (b) a rigid support member carried bysaid frame; (c) a plurality of elongated inflatable sacks, each saidsack being disposed to extend transversely across said support member;(d) at least one of said elongated inflatable sacks having:(i) a pair ofend chambers, each end chamber disposed at an opposite end of said sackand being separately pressurizable, (ii) a pair of intermediate chambersdisposed between said end chambers, each said intermediate chamberhaving a right pentahedron shape with the diagonal surface facing towardthe center of said elongated inflatable sack, and (iii) a firstrestrictive flow passage connecting one of said end chambers to saidadjacent intermediate chamber, and a second restrictive flow passageconnecting said second of said pair of end chambers to said second ofsaid pair of intermediate chambers; and (e) means for maintaining apredetermined pressure in each end chamber of each said elongatedinflatable sack having same.
 12. An apparatus as in claim 11, whereinsaid predetermined pressure maintaining means for each end chamberincludes:(a) a first pressure control valve communicating with at leastone of said pair of end chambers; (b) a second pressure control valvecommunicating with at least the other of said pair of end chambers; (c)a first pressure sensing device for sensing the pressure provided to atleast one of said pair of end chambers; (d) a second pressure sensingdevice for sensing the pressure provided to at least the other of saidpair of end chambers; and (e) a microprocessor connected to saidpressure sensing devices for receiving signals from same and connectedto control said pressure control valves according to said signals fromsaid pressure sensing devices.
 13. An apparatus as in claim 11, furthercomprising:(a) a source of pressurized air for supplying air to saidinflatable sacks; (b) a flow diverter valve having:(i) a first inlet anda second inlet, (ii) a first outlet and a second outlet, (iii) a firstpath connecting said first inlet to said first outlet, (iv) a secondpath connecting said second inlet to said second outlet, and (v) meansfor switching said paths such that said first path connects said firstinlet to said second outlet and said second path connects said secondinlet to said first outlet; (c) a first pressure control valve having afirst output end communicating with one of said inlets and having afirst input end communicating with said source of pressurized air; and(d) a second pressure control valve having a second output endcommunicating with the other of said inlets and having a second inputend communicating with said source of pressurized air.
 14. An apparatusas in claim 11, further comprising:means for setting said predeterminedsack pressure according to the angle of inclination of an articulatablesection of said support member.
 15. An apparatus for supporting apatient, the apparatus comprising:(a) a pair of separately pressurizableend chambers, each end chamber disposed at an opposite end of said sackand having an air sack entrance opening therethrough, (b) a pair ofintermediate chambers disposed between said end chambers, each saidintermediate chamber having a right pentahedron shape with the diagonalsurface facing toward the center of the apparatus, and (c) a firstrestrictive flow passage connecting one of said end chambers to saidadjacent intermediate chamber, and a second restrictive flow passageconnecting said second of said pair of end chambers to said second ofsaid pair of intermediate chambers.
 16. An apparatus as in claim 18,wherein:each said intermediate chamber has a base wall, an altitudewall, a diagonal wall and two opposed triangular-shaped side walls, eachsaid base, altitude and diagonal wall having a generally rectangularshaped perimeter, said base wall being connected at a right angle tosaid altitude wall, said diagonal wall being connected at one edge tosaid base wall and at an opposite edge to said altitude wall, the edgesof each said triangular side wall being connected to edges of said basewall, said diagonal wall, and said altitude wall.
 17. An apparatus as inclaim 16, wherein:each said diagonal wall of each said intermediatechamber is disposed facing said diagonal wall of said other intermediatechamber.
 18. An apparatus as in claim 17, wherein:a single web extendsdiagonally within said sack to separate said intermediate chambers anddefine both said diagonal walls of both said intermediate chambers. 19.An apparatus as in claim 16, wherein:said base wall of one of saidintermediate chambers is disposed adjacent one of said end chambers andsaid base wall of said second of said pair of intermediate chambers isdisposed adjacent said second of said pair of end chambers.
 20. Anapparatus as in claim 19, wherein:said first restrictive flow passage isconnected to said base wall of one of said intermediate chambers, andsaid second restrictive flow passage is connected to said base wall ofsaid second of said pair of intermediate chambers.
 21. An apparatus asin claim 15, further comprising:an elongated coupling having an axialopening therethrough, said coupling secured to said sack entranceopening and extending outwardly therefrom, said coupling configured witha second groove defined around the exterior thereof and configured toreceive a deformable 0-ring therein when said coupling is inserted intoa mateable fitting in airtight engagement with said fitting.